I know the 16" 206 high speed motor in the 70mm dropout spacing is unique to
Power in Motion because the owner had 4 specially built. I'm not sure if the standard version of 16" x 70mm dropout motor [209 motor] is the same as has been used on the Brompton in the past. The batteries and speed controllers may be different as well.
Do you have any links to the Brompton e-bike kit? I'd be curious to read up on it and see what reviewers were saying?
I don't know much about it, just that it exists.
http://www.poweridestore.com/Folding...Conversion-Kit